Genetic Assessment of Potential Source Populations for the Reintroduction of Northern Leopard Frogs (Rana pipiens) to Sites in Alberta.pdf
Gregory A. Wilson, Tara L. Fulton, Kris Kendell, Garry Scrimgeour, Cynthia A. Paszkowski, David W. Coltman
Population persistence is often dependent upon immigration. As habitat loss and fragmentation increase, movement corridors are lost and movement of individuals between populations is reduced or eliminated. Populations may then be extirpated without the possibility of re-establishment through natural means. In such cases, human-mediated translocation may be required to reintroduce a species to parts of its historical range where appropriate, unoccupied habitat exists. Despite the fact that the source population can affect reintroduction success, genetic background is rarely considered when source populations are chosen. The northern leopard frog (Rana pipiens Schreber, 1782) underwent a large decline in the western portion of its range during the 1960s and 1970s, and only occurs in 20% of historically occupied sites in Alberta. Many unoccupied sites still appear to offer good habitat, and the absence of northern leopard frogs may reflect their inability to disperse to these locations from surviving populations. Consequently, human-mediated translocation has been proposed. In this study we used three criteria to examine the genetic background of potential sources for translocation: diversity, similarity to the area of reintroduction, and evolutionary history. We genotyped 187 samples and sequenced 812bp of the mitochondrial NADH dehydrogenase 1 gene from 14 Canadian northern leopard frog populations. Nuclear and mitochondrial diversity were highest in frogs from Manitoba and western Ontario, and declined westward. There was no significant relationship between genetic and geographic distance, suggesting genetic drift is a driving force affecting the genetic relationships between populations, with the possibility of local adaptation. Populations separated by more than ~50 km were quite differentiated. Therefore, source populations similar to the original inhabitants of an area scheduled for reintroduction may be difficult to find or nonexistent. Mitochondrial analyses revealed all populations sampled in this study share a recent evolutionary history, belonging to the western clade of this species.
Consequently, we can make the following recommendations for source populations in reintroduction efforts: i) source populations genetically similar to the original inhabitants of a region are ideal. However, these are unlikely to be found outside of fine spatial scales (~50 km), ii) watershed-based measures of distance are not better predictors of genetic distance than linear distances, suggesting that populations within a watershed are not better sources than those in different watersheds, iii) populations within Alberta all have similar levels of genetic diversity and differentiation, so ecological exchangeability may be the most important factor when choosing source populations, iv) choosing eggs from multiple masses will increase the initial genetic diversity in a newly founded population, v) due to their high levels of diversity, populations in Manitoba and Ontario may be good sources if ecologically exchangeable populations can be found, vi) genetic monitoring of recently founded populations will allow their genetic health to be examined through time.